The Colorado Rockies began placing baseballs in a Coors Field humidor in 2002, and the results were almost immediate. Runs scored and home runs have been on a steady decline as the humidor took effect and the Rockies improved their pitching staff:

Season

Runs per game

Home runs per game

2000

14.37

3.02

2001

13.40

3.31

2002

12.21

2.86

2003

11.94

2.84

2004

12.69

2.73

2005

11.09

2.10

2006

10.73

2.07

2007

10.58

2.23

Source: Elias Sports Bureau

STORAGE BEYOND STOGIES

The conditions Settings: 70 degrees, 50% humidity, designed to keep balls within manufacturer specifications for Major League Baseball (5-5 1/4 ounces, 9-9 1/4 inches in circumference).Dimensions: 9 feet wide by 9 feet deep by 7 feet, 6 inches high.Capacity: Approximately 400 baseballs.Materials: The walls and ceiling are 3 1/2 inches thick, made of Styrofoam-insulated panels and coated with aluminum. The floor is concrete with a moisture-resistant surface coating.System: The humidor is heated and cooled by water coils. The humidity is controlled by a computer.

The process When Rockies employees receive a shipment of game balls (usually four to five per season), they put them immediately in the humidor, stamping each box of 12 balls with the date it was received. They also create a test box, pulling balls from miscellaneous boxes. The test balls are weighed and measured each week, and those measurements are sent to Major League Baseball. MLB officials visit periodically to review the system. All the balls from one shipment are stored in the same rack. The humidor has four racks. The balls are used on a first-in, first-out basis. They usually are stored in the humidor for up to two months. On game day, the game balls to be used that day (10 to 12 dozen) are rubbed up with mud in the morning, then placed back in the humidor in a ball bag until they go out to the field with the umpire. All unused game balls are returned to the humidor. Any balls left in the humidor after the season ends are used for spring training.

DENVER  The name "humidor" evokes images of smoke-filled, wood-paneled rooms, a place where hushed deals are made and secrets are traded only with the most trusted of colleagues.

Maybe that's why the Colorado Rockies' humidor, where they store game balls used at their home park, Coors Field, in an attempt to negate the high-flying, hard-to-control effects of Denver's arid climate on baseballs, was such a subject of intrigue when the Rockies began using it for the 2002 season.

"It was kind of funny to hear some of the conjecture — that there was a big tub of water and all the balls were bobbing in the water," says Kevin Kahn, vice president of ballpark operations for the Rockies.

There is in fact just a big, shiny box with a locked door, humming in a hallway a base hit from the Rockies' clubhouse and indistinguishable from the beer-keg cooler humming even louder next to it.

Behind the door are two rows of wire shelving, stacked with boxes of baseballs. Brightly lit, with a climate resembling that of North Carolina in early spring at 70 degrees with 50% humidity, the humidor seems like nothing more a sparsely appointed pantry for a restaurant that serves up a steady diet of fastballs and breaking balls.

"We've made no secret of this," Kahn says, while standing inside the humidor. "We've been open with it. Anybody from the (opposing) teams that wanted to see it, we'll show it to them. I think it just takes a lot of mystery away."

The humidor has taken away Coors Field's reputation as a hitter's paradise and a pitcher's purgatory. For a time, especially when Blake Street Bombers Dante Bichette, Vinny Castilla, Andres Galarraga and Larry Walker were batting for the Rockies, the park was known as Coors Canaveral.

The number of home runs hit at Coors Field has dropped from 268 in 2001, tops at major league ballparks, to 185 this season, which ranks 10th. Runs overall are down as well, from 13.4 per game in 2001 to 10.58 this season, according to the Elias Sports Bureau.

"This is a desirable place to play now for pitchers," says Colorado reliever Matt Herges, who signed as a free agent in February. Rockies bullpen pitchers can tell when they're warming up with a ball not stored in the humidor.

Although the Rockies have used the humidor for six seasons, its postseason debut came last week, when the Rockies clinched the National League Division Series with a 2-1 win against Philadelphia.

The NL Championship Series comes to Coors Field on Sunday. As fellow-NL West dwellers, the Diamondbacks are no strangers to the humidor-stored balls.

"It has made a difference, without a doubt," says Arizona outfielder Eric Byrnes, a eight-year veteran who played for Colorado in 2005. "Look at the numbers. It's the humidor, and they have a lot better pitching than they used to have."

The idea for the humidor bubbled up during a duck hunt six years ago. Tony Cowell, who works in the Rockies' engineering department, noticed that his leather hunting boots had constricted over the summer. He began to think about the leather covering on baseballs and how the dry air in Denver, where humidity rarely exceeds 10%, affected it.

Rockies employees conducted some basic tests. They dropped balls they'd had in storage for a while from the same height as balls they'd just received from Rawlings, Major League Baseball's supplier, and noted how much higher the older balls bounced. They started weighing balls periodically.

"You could tell over time that it was weighing less and less, to the point of being too light and not meeting Major League Baseball specifications," Kahn says.

Some balls weighed a full ounce less than the 5 to 5 1/4 ounces that MLB requires, he says.

In addition to being lighter, the balls were hard to grip, which was well-known among pitchers around the league.

"I just remember being horrified," Herges says of his first time pitching at Coors Field. "Everybody talked about it. Then when I came, and you play catch down the line first, and it was not like anything I'd ever experienced. The ball would cut. I'd try to throw a curveball and it would just spin."

The Rockies approached MLB with the idea for the humidor. They've fine-tuned the concept and settings over the years.

When they first started using balls stored in the humidor at the beginning of the 2002 season, they didn't tell their own players.

"I was hitting balls and they weren't going out of the yard," Rockies first baseman Todd Helton says. "I was wondering what the heck was going on. I thought something wrong with my swing or whatever, and then a few weeks into the season they told us and it started to make sense."

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Rockies engineer Tony Cowell checks out baseballs in Coors Field's humidor in 2002. The idea for adding moisture to balls bubbled up when Cowell noticed that his leather boots had constricted in the summer, making him think about the leather covering on baseballs and Denver's dry air.

By Ed Andrieski, AP

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